This invention relates to electronic musical instruments, and, more particularly, to an automatic sustain control circuit for producing a pseudo-reverberation effect in electronic organs.
Reverberatinon effects have been achieved in electronic organs in a variety of ways, a common reverberation device including one or more elongated coil springs having an input signal transducer connected at one end thereof to which electrical musical signals to be reverberated are applied, and an output transducer at the other end for converting distortion of the spring caused by the signal back into an electrical signal which is amplified and acoustically reproduced along with the original main signal, either in a common speaker or in a separate reproducing channel. Such devices, although producing a useful reverberation effect, are bulky and difficult to package in the console of electronic organs, and are incapable of reproducing the reverberation effect of a real room, for example.
Also known are reverberation devices utilizing recording and delayed playback of electrical signals corresponding to the music to be reverberated. Such devices, which may utilize a loop of tape and spaced recording and playback heads to achieve the desired delay, produce reasonably acceptable reverberation effects, but they tend to be relatively expensive and to have unacceptable reliability due to wear of the tape and heads.
It is also known that by providing the electronic organ with circuitry that causes the played notes of the organ to have a relatively long decay envelope, an effect that is not unlike reverberation is produced, particularly if the organist plays in a legato manner, namely, smooth and flowing, with unbroken transitions between successive notes, and which in some respects is superior to the reverberation effect achieved with the described spring devices in that it does not have the raggedness in frequency response that characterizes all spring units. However, most electronic organs in use today employ continuously operating tone generators to produce signals corresponding to the various notes of the scale, with each individual tone generator connected to a gating circuit operated in response to application of a DC voltage from the keyboard; that is, when a key is depressed the DC voltage is applied to the associated gating circuit which connects the corresponding tone to the output system of the organ, usually by way of various filters and stop control devices. The gating circuit includes a resistor that determines the attack characteristic and a capacitor so connected that when the key switch corresponding to a given note is closed the capacitor is discharged through a resistor with a predetermined time constant; the time constant for regular organ voices is of such a value that gating occurs with a smooth rise and fall of the intensity at the output of the gate, but without any appreciable sustain characteristic. If, on the other hand, it is desired to simulate chimes or bells, or other percussion instruments, it is known to employ a short attack time constant and a long decay time constant; that is, the capacitor connected to the keying terminal charges quickly and discharges slowly, allowing the tone to build rather quickly, but without a click, and to stay at that level as long as the key is depressed and to decay, upon release of the key, with a generally logarithmic decay curve.
When the just-described long decay time constant is used, and the organ is played in a legato manner, a pseudo-reverberation effect, due to the intermingling of the sounds as one note is played and then released and another note is sounded, results; the sounds intermingle in much the same way as they would in a "live" room in which reverberation causes the notes to continue sounding for a period of time after the keys causing those notes to sound are released. The illusion of real or natural reverberation tends to be destroyed upon release of all played keys, the decay characteristic under such conditions sounding more like the decay characteristic of a percussion instrument.
It is a primary object of the present invention to avoid the described shortcomings of the prior art and to provide means for more effectively using the sustain characteristic to produce an improved pseudo-reverberation effect at very low cost.